Blender Python: Custom Enum Flags
The reason my enums were not showing up was due to me changing my property definitions to use the ':' operator instead of '=', such as..

bpy.types.collection.FBXGSpawner : EnumProperty(


instead of..

bpy.types.collection.FBXGSpawner = EnumProperty(


I read that we are supposed to use the ':' operator in Blender 2.8+. If this is the case, maybe someone can help point out what else I may have done wrong to prevent properties from drawing. One of my simple drawing functions..

# draw object settings
def draw(self, contex):
    aobject = bpy.context.object
    layout = self.layout
    box = layout.box()
    con = box.row()
    con.prop(aobject, "MergeWith")


If anyone knows the reason they were not rendering, post and I will accept it as the answer. Thanks!

Edit: After playing around with the code, I believe this is (at least close) to the correct way to set up a custom enum:

class FBXG_MappingPanel(bpy.types.Panel):

    # define enum flags
    EnumTypes=[ ('GA', "Asset", "tooltip"),
                ('LP', "Low", "tooltip"),
                ('HP', "High", "tooltip"),
                ]

    # define enum variable
    EnumVariable= bpy.props.EnumProperty(
        name="Title",
        options={'ENUM_FLAG'},
        items=EnumTypes,
        description="tooltip",
        )

    # define drawing section
    def draw(self, context):

        # draw
        layout = self.layout
        row = layout.row()
        row.prop_enum(self, "EnumVariable", 'GA', text='Asset')
        row.prop_enum(self, "EnumVariable", 'LP', text='Low')
        row.prop_enum(self, "EnumVariable", 'HP', text='High')


The biggest mistake I made was not realizing that you need an individual prop_enum() call for each individual flag allowed to be selected. I was trying to use it as a single call. If anyone notices any issues here, that would be appreciated. Also, if anyone can help newcomers understand what the number property is intended for and what purpose it serves, that would also be great. Thanks!